Batteries are used in a wide variety of products and systems, and many batteries are rechargeable. For example, Lithium ion (Li-ion) batteries are used in various products and offer high energy density and economy compared to other existing mobile and backup power supply solutions. However, the chemistry of Li-ion battery technology is limited with respect to electromotive force (EMF). As a result, multiple Li-ion cell batteries are often connected in series with one another in an array or battery pack to support high voltage applications like hybrid or Battery Electric Vehicles (BEVs), energy storage systems, and the like. In operation, a set or stack of series-connected cell batteries are subjected to discharging to drive a load, as well as charging operations. In addition, voltage balancing operations and systems have been developed to balance the voltages of the individual cell batteries to extend operational life of the battery pack. The cell balancing can be accomplished by transferring charge from one cell battery in a stack to another stack cell battery, or by transferring charge between a cell battery and an external battery dedicated to charging and discharging operations for cell balancing or other purposes.
Various cell balancing approaches have been developed, including passive balancing and active balancing solutions. Passive balancing involves discharging cells with a higher or highest voltage, and passive balancing is generally cost effective compared with active solutions. However, the efficiency and performance of passive balancing is generally poor compared to active approaches. Some active balancing solutions use DC-DC converters and transformers to transfer energy from one battery to another. For stacks of multiple batteries, bulky active balancing circuitry is often required, due to the large number of cells connected in series for high voltage applications. As a result, active balancing systems are typically higher cost compared with passive balancing solutions.